The present invention relates to a new and improved construction of gas-blast switch.
In its more specific aspects the gas-blast switch of the present development is of the type comprising a pump cylinder which is conjointly mobile along with a movable contact element, this pump cylinder enclosing a pump chamber containing extinguishing gas and feeding a blast nozzle. Within the pump cylinder there is displaceably arranged a pump piston which, during the course of the cutoff stroke, forces the extinguishing gas out of the pump chamber through the blast nozzle.
With such switches it is desired that a certain excess pressure (precompression) already prevails in the pump chamber when the movable contact element, during the course of the cutoff stroke, disengages from the first contact piece, i.e., when the arc ignites, so that from this point in time there is accomplished blowing of the arc.
With many heretofore known switches of this type this is achieved, in that, on the one hand, the pump piston is stationarily supported and, on the other hand, the contacts first separate after there has been accomplished a certain initial displacement path of the cutoff stroke, while the fixed contact piece or element retains the blast nozzle closed until completion of this initial displacement path. With these switches the precompression of the extinguishing gas occurs simultaneous with the cutoff stroke and precedes in time approximately proportionally to the path through which the movable contact element moves during the aforementioned initial displacement path.
With another state-of-the-art switch, as disclosed for instance in German Pat. No. 2,245,423, the pump cylinder, and therefore the movable contact element, is coupled by means of a connecting rod at a first crank arm and the pump piston is coupled by means of a further connecting rod at a second crank arm. Both crank arms are fixedly seated for rotation upon a common shaft and enclose therebetween an angle. In the cuton position both crank arms extend away from one another and upwardly at an inclination. For cutoff the shaft is rotated in the sense that the second crank arm, operatively associated with the pump piston, must initially attain its upper dead-center position, while the first crank arm, operatively associated with the pump cylinder, directly strives to reach its lower dead-center position. Here, the precompression likewise occurs simultaneous with the start of the cutoff stroke, however to a more intensified degree than such otherwise would be the case by virtue of the starting displacement path through which there moves the movable contact element during the cutoff stroke.
The precompression of the extinguishing gas requires a drive energy which must be expended by the switch drive. However, the switch drive, also at the start of the cutoff stroke, must accelerate the movable parts of the switch out of its stationary state. On the other hand, the precompressed extinguishing gas is first needed at that point in time when the movable contact element separates from the fixed contact.